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Yia-Chung Chang

Bio: Yia-Chung Chang is an academic researcher from Academia Sinica. The author has contributed to research in topics: Exciton & Quantum dot. The author has an hindex of 48, co-authored 474 publications receiving 9213 citations. Previous affiliations of Yia-Chung Chang include University of Illinois at Urbana–Champaign & National Cheng Kung University.


Papers
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Journal ArticleDOI
TL;DR: In this article, temperature-dependent Hall-effect measurements were carried out both in dark and in ambient light on Si-doped layers grown by molecular-beam epitaxy over the entire composition range.
Abstract: Temperature-dependent Hall-effect measurements were carried out both in dark and in ambient light on Si-doped ${\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}$ layers grown by molecular-beam epitaxy over the entire composition range. Above 150 K, the measured Hall carrier densities (different from actual electron densities near the direct-indirect transition) show an exponential dependence on temperature. A shallow donor (\ensuremath{\le}15 meV) tied to the $\ensuremath{\Gamma}$ band and a deep donor level tied to the $L$ band were observed. The deep donor is dominant for $xg0.2$, and its activation energy ${E}_{d}$ rises dramatically up to the direct-indirect band-gap crossover and peaks at 160 meV for $x\ensuremath{\sim}0.48$. As the A1 fraction increases further, ${E}_{d}$ decreases, reaching 57 meV for AlAs. The error due to multivalley conduction on the measured values of ${E}_{d}$ is shown to be negligible. The variation in ${E}_{d}$ of the dominant donor level with $x$ is accounted for by our theoretical calculations using a multivalley effective-mass model. A decrease of ${E}_{d}$ with increasing doping densities is also observed. At high substrate-growth temperature, the incorporation of Si atoms was found to decrease. The persistent-photoconductivity (PPC) effect was observed with an increase in mobilities over the dark values in the entire composition range. The effect was most pronounced in the range $0.20\ensuremath{\le}x\ensuremath{\le}0.40$. Traps related to the Si-doping density appear to be responsible for the observed photoconductivity effect. The ratio of the PCC traps and the Si atomic density is maximum at $x\ensuremath{\sim}0.32$ and is minimum in the direct-indirect band-gap crossover region.

312 citations

Journal ArticleDOI
TL;DR: The radiative lifetimes of excitons in quantum wires are estimated and it is found that the lifetime of the shortest-lived exciton ranges from 57 ns to 170 \ensuremath{\mu}s for wire widths from 7.7 to 31 A\r{}.
Abstract: We present theoretical studies of the electronic and optical properties of free-standing Si quantum wires which exist in porous Si. We use a second-neighbor empirical tight-binding model which includes d orbitals and spin-orbit interaction. The excitonic effects are included within the effective-mass approximation. We found that for narrow quantum wires with widths around 8 A\r{}, the averaged exciton oscillator strength is comparable to that of bulk GaAs. However, the average exciton oscillator strength decreases dramatically (faster than 1/${\mathit{L}}^{5}$) as the quantum-wire width L increases. The radiative lifetimes of excitons in quantum wires are estimated and we find that the lifetime of the shortest-lived exciton ranges from 57 ns to 170 \ensuremath{\mu}s for wire widths from 7.7 to 31 A\r{}. We have also calculated the absorption spectra and found strong polarization dependence.

284 citations

Journal ArticleDOI
TL;DR: In this paper, the energy spectrum of the ground state and the low-lying excited states for shallow donors in quantum well structures consisting of a single slab of GaAs sandwiched between two semi-infinite layers of
Abstract: We present the results of a study of the energy spectrum of the ground state and the low-lying excited states for shallow donors in quantum well structures consisting of a single slab of GaAs sandwiched between two semi-infinite layers of ${\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{Al}}_{x}\mathrm{As}$. The effect of the position of the impurity atom within central GaAs slab is investigated for different slab thicknesses and alloy compositions. Two limiting cases are presented: one in which the impurity atom is located at the center of the quantum well (on-center impurity), the other in which the impurity atom is located at the edge of the quantum well (on-edge impurity). Both the on-center and the on-edge donor ground state are bound for all values of GaAs slab thicknesses and alloy compositions. The alloy composition $x$ is varied between 0.1 and 0.4. In this composition range, ${\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{Al}}_{x}\mathrm{As}$ is direct, and the single-valley effective-mass theory is a valid technique for treating shallow donor states. Calculations are carried out in the case of finite potential barriers determined by realistic conduction-band offsets.

229 citations

Journal ArticleDOI
TL;DR: By manipulating the ratios and disk sizes, a high-performance, wide-angle, polarization-independent dual band absorber was experimentally achieved and demonstrated a substantial flexibility in absorber designs for applications in thermal photovoltaics, sensors, and camouflage.
Abstract: Two-dimensional metallic broadband absorbers on a SiO(2)/Ag/Si substrate were experimentally studied. The absorptivity of such structure can be increased by tailoring the ratio of disk size to the unit cell area. The metallic disk exhibits a localized surface plasmon polariton (LSPP) mode for both TE and TM polarizations. A broadband thermal emitter can be realized because the LSPP mode is independent of the periodicities. By manipulating the ratios and disk sizes, a high-performance, wide-angle, polarization-independent dual band absorber was experimentally achieved. The results demonstrated a substantial flexibility in absorber designs for applications in thermal photovoltaics, sensors, and camouflage.

213 citations

Journal ArticleDOI
TL;DR: The relationship between the superlattice electronic wave functions and band structure to those of the two bulk semiconductors from which it is constructed is studied within the framework of the empirical tight-binding model, which is solved using the reduced Hamiltonian technique.
Abstract: Much understanding of the electronic and optical properties of a semiconductor superlattice can be obtained by relating the superlattice electronic wave functions and band structure to those of the two bulk semiconductors from which it is constructed. In this paper, the relationship is studied within the framework of the empirical tight-binding model, which is solved using the reduced Hamiltonian technique. The superlattice wave functions are described as linear combinations of bulk Bloch functions with complex wave vectors, twenty (including spin) for each of the two constituent materials. The bulk Bloch-function composition of the superlattice wave function is studied as a function of layer thickness, alloy composition, and energy. The GaAs-${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Al}}_{\mathrm{x}}$As and InAs-GaSb superlattices are examined in detail. Comparisons with simpler Kronig-Penney and envelope-function models are made. It is found that the lowest superlattice conduction-band states are primarily derived from the expected bulk states with wave vectors near the center of the Brillouin zone, with a small admixture of zone-edge components. The energies and general form of the wave functions are modified only slightly, except close to the interfaces. There, the admixture can significantly affect the interfacial boundary conditions beyond those employed by commonly used envelope-function approximations. Valence-band states are more complicated in that the superlattice periodic potential mixes the bulk heavy-hole, light-hole, and spin-orbit split-off bands, even at the superlattice Brillouin-zone center. Crossover effects occur in which a given superlattice subband can have a varying proportion of light-hole-like or heavy-hole-like character depending on superlattice layer thickness. The dispersion of the subbands away from the zone center also causes the mixing of bands and results in modifications of the superlattice band structure as compared with band structures produced by simpler models.

184 citations


Cited by
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Journal ArticleDOI
TL;DR: In this article, the authors present a comprehensive, up-to-date compilation of band parameters for the technologically important III-V zinc blende and wurtzite compound semiconductors.
Abstract: We present a comprehensive, up-to-date compilation of band parameters for the technologically important III–V zinc blende and wurtzite compound semiconductors: GaAs, GaSb, GaP, GaN, AlAs, AlSb, AlP, AlN, InAs, InSb, InP, and InN, along with their ternary and quaternary alloys. Based on a review of the existing literature, complete and consistent parameter sets are given for all materials. Emphasizing the quantities required for band structure calculations, we tabulate the direct and indirect energy gaps, spin-orbit, and crystal-field splittings, alloy bowing parameters, effective masses for electrons, heavy, light, and split-off holes, Luttinger parameters, interband momentum matrix elements, and deformation potentials, including temperature and alloy-composition dependences where available. Heterostructure band offsets are also given, on an absolute scale that allows any material to be aligned relative to any other.

6,349 citations

Journal ArticleDOI
TL;DR: In this article, the most characteristic properties of spin glass systems are described, and related phenomena in other glassy systems (dielectric and orientational glasses) are mentioned, and a review summarizes recent developments in the theory of spin glasses, as well as pertinent experimental data.
Abstract: This review summarizes recent developments in the theory of spin glasses, as well as pertinent experimental data. The most characteristic properties of spin glass systems are described, and related phenomena in other glassy systems (dielectric and orientational glasses) are mentioned. The Edwards-Anderson model of spin glasses and its treatment within the replica method and mean-field theory are outlined, and concepts such as "frustration," "broken replica symmetry," "broken ergodicity," etc., are discussed. The dynamic approach to describing the spin glass transition is emphasized. Monte Carlo simulations of spin glasses and the insight gained by them are described. Other topics discussed include site-disorder models, phenomenological theories for the frozen phase and its excitations, phase diagrams in which spin glass order and ferromagnetism or antiferromagnetism compete, the Ne\'el model of superparamagnetism and related approaches, and possible connections between spin glasses and other topics in the theory of disordered condensed-matter systems.

3,926 citations

Proceedings Article
14 Jul 1996
TL;DR: The striking signature of Bose condensation was the sudden appearance of a bimodal velocity distribution below the critical temperature of ~2µK.
Abstract: Bose-Einstein condensation (BEC) has been observed in a dilute gas of sodium atoms. A Bose-Einstein condensate consists of a macroscopic population of the ground state of the system, and is a coherent state of matter. In an ideal gas, this phase transition is purely quantum-statistical. The study of BEC in weakly interacting systems which can be controlled and observed with precision holds the promise of revealing new macroscopic quantum phenomena that can be understood from first principles.

3,530 citations

Book
01 Jan 2004
TL;DR: In this paper, the Kohn-Sham ansatz is used to solve the problem of determining the electronic structure of atoms, and the three basic methods for determining electronic structure are presented.
Abstract: Preface Acknowledgements Notation Part I. Overview and Background Topics: 1. Introduction 2. Overview 3. Theoretical background 4. Periodic solids and electron bands 5. Uniform electron gas and simple metals Part II. Density Functional Theory: 6. Density functional theory: foundations 7. The Kohn-Sham ansatz 8. Functionals for exchange and correlation 9. Solving the Kohn-Sham equations Part III. Important Preliminaries on Atoms: 10. Electronic structure of atoms 11. Pseudopotentials Part IV. Determination of Electronic Structure, The Three Basic Methods: 12. Plane waves and grids: basics 13. Plane waves and grids: full calculations 14. Localized orbitals: tight binding 15. Localized orbitals: full calculations 16. Augmented functions: APW, KKR, MTO 17. Augmented functions: linear methods Part V. Predicting Properties of Matter from Electronic Structure - Recent Developments: 18. Quantum molecular dynamics (QMD) 19. Response functions: photons, magnons ... 20. Excitation spectra and optical properties 21. Wannier functions 22. Polarization, localization and Berry's phases 23. Locality and linear scaling O (N) methods 24. Where to find more Appendixes References Index.

2,690 citations

Journal ArticleDOI
TL;DR: In this article, a review of the properties of the Al x Ga1−x As/GaAs heterostructure system is presented, which can be classified into sixteen groups: (1) lattice constant and crystal density, (2) melting point, (3) thermal expansion coefficient, (4), lattice dynamic properties, (5) lattices thermal properties,(6) electronic-band structure, (7) external perturbation effects on the bandgap energy, (8) effective mass, (9) deformation potential, (10) static and
Abstract: The Al x Ga1−x As/GaAs heterostructure system is potentially useful material for high‐speed digital, high‐frequency microwave, and electro‐optic device applications Even though the basic Al x Ga1−x As/GaAs heterostructure concepts are understood at this time, some practical device parameters in this system have been hampered by a lack of definite knowledge of many material parameters Recently, Blakemore has presented numerical and graphical information about many of the physical and electronic properties of GaAs [J S Blakemore, J Appl Phys 5 3, R123 (1982)] The purpose of this review is (i) to obtain and clarify all the various material parameters of Al x Ga1−x As alloy from a systematic point of view, and (ii) to present key properties of the material parameters for a variety of research works and device applications A complete set of material parameters are considered in this review for GaAs, AlAs, and Al x Ga1−x As alloys The model used is based on an interpolation scheme and, therefore, necessitates known values of the parameters for the related binaries (GaAs and AlAs) The material parameters and properties considered in the present review can be classified into sixteen groups: (1) lattice constant and crystal density, (2) melting point, (3) thermal expansion coefficient, (4) lattice dynamic properties, (5) lattice thermal properties, (6) electronic‐band structure, (7) external perturbation effects on the band‐gap energy, (8) effective mass, (9) deformation potential, (10) static and high‐frequency dielectric constants, (11) magnetic susceptibility, (12) piezoelectric constant, (13) Frohlich coupling parameter, (14) electron transport properties, (15) optical properties, and (16) photoelastic properties Of particular interest is the deviation of material parameters from linearity with respect to the AlAs mole fraction x Some material parameters, such as lattice constant, crystal density, thermal expansion coefficient, dielectric constant, and elastic constant, obey Vegard’s rule well Other parameters, eg, electronic‐band energy, lattice vibration (phonon) energy, Debye temperature, and impurity ionization energy, exhibit quadratic dependence upon the AlAs mole fraction However, some kinds of the material parameters, eg, lattice thermal conductivity, exhibit very strong nonlinearity with respect to x, which arises from the effects of alloy disorder It is found that the present model provides generally acceptable parameters in good agreement with the existing experimental data A detailed discussion is also given of the acceptability of such interpolated parameters from an aspect of solid‐state physics Key properties of the material parameters for use in research work and a variety of Al x Ga1−x As/GaAs device applications are also discussed in detail

2,671 citations